This research project is on the structure-function relationships of C-reactive protein (CRP) in rheumatoid arthritis (RA) and is focused on the interaction between modified CRP and immune complexes (ICs) and on the possible role of modified CRP in regulating IC-mediated inflammatory responses and development of RA. RA is an autoimmune disease in which autoantibody-mediated inflammation leads to erosive destruction of the joints. CRP is a plasma protein but is also present in the synovial fluid of RA patients. The functions of CRP in RA and whether CRP is always functional while in the synovial fluid are unknown. Immune complexes have been implicated in promoting RA inflammation, in part due to complement activation by ICs and in part due to the binding of ICs to phagocytes resulting in the production of pro-inflammatory cytokines. Using the collagen- induced arthritis (CIA) mouse model of RA, it has been shown that CRP exerts a protective effect during the onset of CIA via undefined mechanisms. We hypothesize that CRP requires a change in its structure and that modified CRP binds to ICs and subsequently controls the pro-inflammatory effects of ICs. Because RA patients are more susceptible to cardiovascular disease and because modified CRP also binds to atherogenic low- density lipoprotein (LDL), we hypothesize that modified CRP also controls the pro-inflammatory effects of LDL and can protect against the development of atherosclerosis. Accordingly, the effects of three different exogenously prepared CRP variants on the development of CIA and atherosclerosis in mice will be investigated. These structurally altered CRP variants are: H2O2-treated CRP and two CRP mutants generated by site-directed mutagenesis. These CRP variants, unlike native CRP, are capable of binding to immobilized ICs and atherogenic LDL. Therefore, it is anticipated that the administration of these CRP variants into mice will result in the decrease in complement activation and production of pro-inflammatory cytokines, and that the CRP variants will be more protective than native CRP against the development of CIA and atherosclerosis in mice. In aim 1, we will determine whether exogenously prepared modified CRP capable of binding to ICs is protective against the development of CIA in mice. In aim 2, we will determine whether the binding of modified CRP to ICs reduces the pro-inflammatory effects of ICs. In aim 3, we will determine whether modified CRP capable of binding to atherogenic LDL is protective against the development of atherosclerosis in mice. The overall goal is to provide insight into the possible use of modified CRP in controlling autoantibody-mediated and LDL-mediated inflammation in the joints of RA patients and in the arteries of atherosclerosis patients, respectively, and may open a new line of investigation to explore why endogenous CRP fails to prevent the development of inflammatory diseases.